1. Field of the Invention
The present invention relates to flattening a workpiece support surface comprised of loose granular material, and, more particularly, to a method and apparatus for spreading loose granular refractory material comprising a refractory bed contained in a transport car for a workpiece incident to heat treating in a furnace.
2. Description of the Prior Art
Heat treating furnaces are utilized in various stages of the production of metal products, and are utilized to perform treatments such as stress relieving, tempering, hardening, decarburizing, and annealing of metal workpieces particularly, coiled strip.
One type of heat treating furnace is a tunnel furnace as disclosed in U.S. Pat. No. 3,778,221, issued December 11, 1973. A coil of metal strip material or other workpiece to be treated is placed on a wheeled furnace car and carried thereby through the furnace which has the form of a long tunnel. The coil of metal strip is arranged with edge convolutions of the coil forming the load bearing surface for the coil. A sufficient number of furnace cars, each bearing a coil of metal strip, are inserted into the furnace in a sequential manner. As each furnace car enters the furnace, cars already residing therein are pushed further into the furnace. Once the furnace fills with these cars, each additional car inserted into the furnace results in a furnace car being pushed out of the furnace at the other end.
The tunnel furnace is typically operated at temperatures approaching two thousand degrees Fahrenheit. Because the furnace car and the coil of metal strip are heated, it was found that a steel base plate forming a carrier for the coil on the car underwent thermal distortions, causing damage to the edge of the coil supported by the base plate (such damage oftentimes descriptively referred to as "oil canning"). It has been discovered that the elimination of distortions to the steel floor plate did not avoid the same type of damage to the edge of the coil.
A refractory material is positioned on the load bearing floor of each furnace car. Sand has been used in the past, but a refractory material comprised of zirconia pebbles, referred to as a zirconia bubble bed, is now frequently employed.
When a bubble bed is used to support a coil of strip on the floor plate of the furnace car, if the refractory pebbles form an uneven coil support area, the bottom edge of the coiled strip is damaged. Prior to the placement of the coil on the refractory bubble bed, attempts are made to ensure that the refractory bed surface is flat. Presently, the refractory bubble bed is flattened and leveled visually by operating personnel using a hand-held push broom. A completely flat and level refractory bed surface is rarely obtained in this manner.
It is therefore the object of the present invention to provide an apparatus and method for flattening and/or leveling a bed surface of granular material used to support a workpiece for processing such as a heat treating operation.